The present invention relates to a device for delivering ink, more particularly to a print head for an ink jet printer, provided with a series of ink delivery nozzles which can be actuated selectively for printing a sheet of paper or the like. The present invention also relates to an ink jet printer provided with such a print head.
A device of this kind is known, inter alia, from U.S. Pat. No. 4,364,067. In one embodiment, the print head comprises a base member or plate, which is substantially triangular in cross-section, and which is disposed with the apex extending towards the paper for printing and has at its top, two ink inlets situated at the top ends of the oblique sides and connected to an ink reservoir. Each of the ink inlets leads into an ink distribution chamber, to which are connected a plurality of ducts formed in the associated oblique side. In the plane of the associated oblique side these ducts converge with an arc towards a number of obliquely extending ink delivery nozzles. The ducts are each provided with a constriction and a pressure chamber situated directly downstream thereof. The ducts are covered by a vibrating plate on which an electrode is disposed. At the pressure chambers piezo-electric elements provided with an electrode are mounted on the first-mentioned electrode. By selective actuation of the piezo-electric elements the vibrating plate is pressed in locally and the volume of the pressure chamber in the required duct is reduced so that a specific quantity of ink is propelled through said duct to the associated ink delivery nozzle.
A disadvantage of the known printer head is that making the ducts in the base member causes considerable trouble and effort.
A comparable difficulty is found in making ink passages in another known printer head, which is provided with a base member or base plate with two flat sides and a head surface, each side being formed with a row of parallel ink ducts which near the corner to the head surface merge into ink tunnels extending through the base member towards the head surface.
According to the present invention, there is provided a device for delivering ink to a sheet of paper or the like, comprising a body with sides and a head surface disposed at an angle to the sides and having therein an inlet for the ink originating from a reservoir. A distribution chamber is provided with a number of ink delivery nozzles situated at the head surface and a plurality of ink passages extend between the distribution chamber and the ink delivery nozzles along one or more of the sides of the body. Means located at the ink passages are provided on that side for selectively propelling ink therethrough to the ink delivery nozzles, wherein the ink passages, over the path from at least the pass-through means to the ink delivery nozzles, are formed as parallel continuous open ducts in the surface of the associated side and the adjoining head surface of the body.
As a result of the parallel configuration and continuous attitude at the surface of the body, the production of the ducts in the associated side and the head surface can take place accurately in a continuous operation by machining in the direction of the ducts. For the machining it is possible for example to use a milling tool with a number of parallel milling discs.
Preferably, the ducts follow a smoothly convexly curved path in the associated side and the adjoining head surface, particularly in the transition zone thereof. As a result, the ink flow is smoother and ink delivery can take place more accurately.
The machining operation can in this way progress more smoothly and any gaps in machining which might result in inaccuracies can be kept to a minimum.
Machining is further simplified if the surfaces of the associated side and the adjoining head surface are smoothly convexly curved at least in the transition zone thereof. In this case, closing the ducts off from the exterior is facilitated since they can be covered by a continuous ink-tight layer, such as a suitable foil, without the foil having to be plastically deformed locally, as would be the situation in the case of a sharp transition.
This layer can easily be given a further function, by having the ink delivery nozzles, which are situated at the downstream ends of the ducts, formed in said ink-tight layer. The number of machining operations on the body can then be kept to a minimum. Parallel with this machining, the ink-tight layer can be prepared and then be applied to the body in one operation.
Further simplification is obtained if the ink propulsion means comprises a plurality of piezo-electric elements operative on the ducts with the ink-tight layer extending between the piezo-electric elements and the ducts.
Since the body does not need any material to form the outward boundary of the ink passages, the latter can be disposed with a smaller center-to-center distance from one another.
In another development of the device according to the present invention, this advantage is enhanced in that the body is provided with two opposite sides in which the ducts are formed, and the ducts in one side are offset from the ducts in the opposite side, the ducts having a conical downstream end. This conical end is produced as if automatically by a milling tool with which the substantially T, V or U-shaped ducts are made, when the tool comes to the end of the ducts. The conical ends of the alternate ducts ensure that the ducts at the delivery end, and hence the ink delivery nozzles, can be situated closer together than would otherwise be the case even if the ink delivery nozzles are situated in line with one another. The result is a denser and hence tighter print pattern on the sheet of paper.